May 16, 1878] 



NATURE 



71 



sonorous {e.g., aluminium, bell metal, steel, standard gold, 

 &c.). 



The chief value of many metals and alloys for indus- 

 trial purposes lies in their possession to a greater or less 



Fig. 4. 



extent of a combination of properties of somewhat 



Fig. 5. 



opposite kinds ; whilst they possess sufficient rigidity to 



keep their shape even with moderately hard usage and 

 to bear "wear and tear," when once fashioned into articles 

 of domestic and everyday use, they have the power of 

 yielding to pressure, &c., to a sufficient extent to enable 

 them to be readily worked into these forms. In some 

 cases the requisite softness for this latter purpose is hardly 

 attained until the temperature is considerably raised ; thus 

 most articles of wrought iron are made when the metal is 

 softened by heat so as to yield readily to percussion 

 {forgoing) and other shaping processes. Closely con- 

 nected with this softening or incipient conversion into a 

 pliable mass by heat, is the phenomenon of welding, or 



the adherence together of two separate metallic masses 

 when united by pressure in such a way as to form a join 



as strong as the other parts. Iron and platinum possess 

 this power at a high temperature ; sodium and some of 



